It is desirable to measure the peak amount of static electricity or “tribocharge” and its characteristic rate of decay on various types of objects or materials (e.g., a plastic packaging material for semiconductor devices). One method for measuring the tribocharge characteristics of materials is to use a non-contact probe associated with a tribocharge meter or electrostatic voltmeter. An amount of electrostatic voltage is deliberately built up on a surface of a piece of material under test by rubbing the surface of the material. The probe measures the amount of built-up charge in a non-contact manner. The rubbing is usually performed manually by a person wearing a nitril glove to generate the electrostatic charge and corresponding voltage on the surface of the test piece.
However, this process of manually rubbing the test piece has several problems associated therewith. For example, the person performing the rubbing will invariably rub the surface of the test piece at various speeds and pressures during the rub time, which could last for a minute or so. Also, the person will likely rub different test pieces at different speeds and pressures such that there is no consistency in the rubbing (and, thus, in the generation and subsequent measurement of the static electricity) from piece to piece. This is primarily because the person performing the test receives no helpful feedback regarding the speed and/or pressure at which that person is rubbing the piece. As a result, the person inherently cannot exert any degree of control over the rubbing process and, thus, inconsistent measurement results inevitably occur. Also, the manual rubbing may induce unwanted noise into the measurement process.
Such poor repeatability and inconsistency of the manual testing process may cause difficulty, for example, in a material qualification process. Also, for some types of plastics with relatively low resistance values, the rate of decay or discharge of the electrostatic buildup on the test piece is too quick for a person to move the test piece fast enough to a position adjacent the measuring probe to accurately capture all of the desired data points in time.
What is needed is a method and apparatus for the automated rubbing of a test piece of material to generate an electrostatic charge on a surface of the test piece and to measure the peak voltage associated with the generated charge along with its ensuing rate of decay or discharge, where the charge generation and subsequent measurement are achieved in a rapid and consistent manner with any one test piece and from piece to piece.